The all-aluminium construction SEADEUCER had built-in flotation which prevented the vessel from sinking after the capsizing. This built-in flotation and the flotation provided by a partially filled fuel tank constituted sufficient buoyancy for the SEADEUCER to remain at the surface after the vessel capsized, allowing the occupants to sit on the overturned hull. The water entering through the transom opening at the end of the dive created a free surface effect which was detrimental to the positive stability of the vessel. When the divers on board began to move from one side to the other, the water quickly followed, thus eliminating any remaining positive stability, and the vessel capsized. After discussing their options, the group decided that two of the stronger swimmers would attempt to reach the shore to obtain help because a large power boat which had passed within 300 m of their overturned vessel had not seen either the vessel or the flares that were fired, the weather was deteriorating and night was falling. There was also a following sea to the shore. It is not known why the power boat did not see the flares, but it is possible that the glare of the afternoon sun prevented the operator of the unidentified craft from seeing the flares and the divers with their arm-waving movements. Day signal flares, such as orange smoke flares, are more persistent and inherently more visible in daylight situations than either the handheld or the rocket-type short-lived, conventional, red, night-time flares. The operator was aware of the broader small craft warning for eastern Lake Ontario, but between 1000 and 1100, the average wind speed had decreased locally from seven to four knots, which may have reassured the operator about proceeding with the dive. Between 1200 and 1300, however, while the dive was in progress, the wind increased significantly to 20 knots, gusting to 30 knots. Also, over open water, the wind speed could be as much as 30 per cent greater than that recorded at land stations. This view has been confirmed by climatologists at Environment Canada. As a result of the capsizing, the owner has now decided to limit the number of persons on board to six, including the operator of the vessel.Analysis The all-aluminium construction SEADEUCER had built-in flotation which prevented the vessel from sinking after the capsizing. This built-in flotation and the flotation provided by a partially filled fuel tank constituted sufficient buoyancy for the SEADEUCER to remain at the surface after the vessel capsized, allowing the occupants to sit on the overturned hull. The water entering through the transom opening at the end of the dive created a free surface effect which was detrimental to the positive stability of the vessel. When the divers on board began to move from one side to the other, the water quickly followed, thus eliminating any remaining positive stability, and the vessel capsized. After discussing their options, the group decided that two of the stronger swimmers would attempt to reach the shore to obtain help because a large power boat which had passed within 300 m of their overturned vessel had not seen either the vessel or the flares that were fired, the weather was deteriorating and night was falling. There was also a following sea to the shore. It is not known why the power boat did not see the flares, but it is possible that the glare of the afternoon sun prevented the operator of the unidentified craft from seeing the flares and the divers with their arm-waving movements. Day signal flares, such as orange smoke flares, are more persistent and inherently more visible in daylight situations than either the handheld or the rocket-type short-lived, conventional, red, night-time flares. The operator was aware of the broader small craft warning for eastern Lake Ontario, but between 1000 and 1100, the average wind speed had decreased locally from seven to four knots, which may have reassured the operator about proceeding with the dive. Between 1200 and 1300, however, while the dive was in progress, the wind increased significantly to 20 knots, gusting to 30 knots. Also, over open water, the wind speed could be as much as 30 per cent greater than that recorded at land stations. This view has been confirmed by climatologists at Environment Canada. As a result of the capsizing, the owner has now decided to limit the number of persons on board to six, including the operator of the vessel. The SEADEUCER was licensed as a pleasure craft and was being operated as a charter boat. There was no information as to the number of persons the boat could carry safely in conjunction with a substantial amount of diving equipment. Although the operator was aware of the overall marine forecast broadcast via VHF radio which issued small craft warnings all day, he may have been reassured about proceeding with the dive after he heard the local radio station weather information. The lull in the wind speed between 1000 and 1100 may have been a factor in the operator's decision to proceed with the dive. The SEADEUCER capsized when water, entering through an opening in the transom, created a free surface effect on the deck, detrimental to the vessel's inherent stability. The free surface effect was compounded by the movement of all those on board to starboard. Several red flares fired in the direction of a power boat passing within an estimated 300 m were ineffective in alerting the attention of the operator to the capsized vessel. The glare of the bright afternoon sun may have prevented the operator of the passing craft from seeing the flares fired from the same direction as the sun. The lifejackets did not float free when the vessel capsized and were relatively inaccessible to those on board because they were stowed in the forward cuddy cabin. The flotation and heat retention provided by the wet suits safeguarded the divers from a more tragic outcome.Findings The SEADEUCER was licensed as a pleasure craft and was being operated as a charter boat. There was no information as to the number of persons the boat could carry safely in conjunction with a substantial amount of diving equipment. Although the operator was aware of the overall marine forecast broadcast via VHF radio which issued small craft warnings all day, he may have been reassured about proceeding with the dive after he heard the local radio station weather information. The lull in the wind speed between 1000 and 1100 may have been a factor in the operator's decision to proceed with the dive. The SEADEUCER capsized when water, entering through an opening in the transom, created a free surface effect on the deck, detrimental to the vessel's inherent stability. The free surface effect was compounded by the movement of all those on board to starboard. Several red flares fired in the direction of a power boat passing within an estimated 300 m were ineffective in alerting the attention of the operator to the capsized vessel. The glare of the bright afternoon sun may have prevented the operator of the passing craft from seeing the flares fired from the same direction as the sun. The lifejackets did not float free when the vessel capsized and were relatively inaccessible to those on board because they were stowed in the forward cuddy cabin. The flotation and heat retention provided by the wet suits safeguarded the divers from a more tragic outcome. The charter dive boat SEADEUCER capsized because of the effect of free surface water on deck and unequal weight distribution. In deteriorating weather, water accumulated on deck when it was shipped through an opening in the transom used to enable the divers to re-board the vessel. The operator did not avail himself of the detailed weather forecast on VHF radio which would have indicated that the lull in the wind experienced between 1000 and 1100 was temporary.Causes and Contributing Factors The charter dive boat SEADEUCER capsized because of the effect of free surface water on deck and unequal weight distribution. In deteriorating weather, water accumulated on deck when it was shipped through an opening in the transom used to enable the divers to re-board the vessel. The operator did not avail himself of the detailed weather forecast on VHF radio which would have indicated that the lull in the wind experienced between 1000 and 1100 was temporary. A Hazard Notification was submitted to the Accident Prevention Group of the TSB, concerning the awareness of boaters to the differences between red night-time flares and orange smoke daytime flares. The facts of the occurrence indicated that the flares were either not seen or ignored.Safety Action Taken A Hazard Notification was submitted to the Accident Prevention Group of the TSB, concerning the awareness of boaters to the differences between red night-time flares and orange smoke daytime flares. The facts of the occurrence indicated that the flares were either not seen or ignored.